Posted
by
kdawson
on Sunday October 29, 2006 @06:54AM
from the turn-toward-the-light dept.

jessiej writes, "Even though copper indium gallium selenide (CIGS), a newer type of solar panel, is less efficient than its silicon counterpart, millions are being invested in manufacturing. From the article: 'CIGS panels use far less raw material than silicon solar panels and the factories themselves cost less to build,' $25 million compared to $230 million in one example. These types of panels could even be made into a t-shirt logo."

Shortages of silicon have crimped sales in the solar industry. Although some analysts have said indium--the "I" in CIGS and a material used in LCD TVs--could be in short supply at some point, executives in the CIGS business have downplayed these concerns. Indium is actually fairly common in the earth, according to Schuyler.

The use of indium increases the bandgap of the CIGS layer, gallium is added to replace as much indium as possible due to gallium's relative availability to indium. Approximately 70% of Indium currently produced is used by the flat-screen monitor industry. Some investors in solar technology worry that production of CIGS cells will be limited by the availability of indium.

I think they intended those measurements to mean they are capable of manufacturing an aggregate number of solar panels capable of generating X megawatts in total annually. In other words, they're stating the total amount of power output they can output in a year.
The confusion arises when the writer attempts to equate the annual output by a CIGS factory (measured in megawatts of power) with the annual output of a coal power plant (measured in megawatt-hours of work). My guess is that they are really stating that a coal power plant can produce 500 MW of power.
Of course this indicates a deeper flaw in the discussion in that a coal power plant can continuously produce 500MW of power (presuming a constant supply of coal). Whereas a solar plant can only produce 500MW of power for half the day.

Yes. Si is the second most abundant element on the surface of the Earth, next to oxygen.

And that's the crux of the problem too. Silica (SiO2) is abundant (quartz sand), but SiO2 is a BITCH to break apart (the usual reaction is with carbon in an almost 2000 deg C arc furnace), you have to partially melt it or transform it into gaseous silanes (e.g., HSiCl3) to remove impurities, and then you have to grow the Si crystals in high temperature furnaces in very clean conditions. Some of the impurities have to be reduced to the parts per billion range for some applications. It is an energy-intensive and expensive process, and the demand for Si for computer chips cuts into supply for solar cells.

If you look at road surfaces, you will see that they are "clean" only in the sense of being free of large scale obstacles. Tire marks, dirt, oil, and other random stuff is all over the road surface.

Solar panels need optical transparency in their protective layer. Keeping roads clean enough to provide that level of optical clarity is just not going to be workable, except possible with nanotechnology.

When we get self rebuilding roadbeds then solar roadbeds might be practical, but for now roofs are much more practical as targets - most are slanted, don't have cars running over them, and get rained on periodically to help with self cleaning.

It is not the efficiency (W/m^2) that needs to go UP in order to make fixed solar generation facilities common, it is the cost ( $/W) that needs to come DOWN.

I'll argue that for a typical small house (1500 sq-Ft) there is more than enough roof area to generate all the electricity for the house, even with 6-7% efficient solar panels. Unfortunately, buying current solar panels, this much energy would cost you >$35,000 !! (And that doesn't include batteries, tracker, inverter.... etc)

If these guys can make lower efficiency panels that also have lower cost/Watt, it is a winning situation for everyone. Where do I buy their stock ?

The nanosolar people claim the panels can be done in a web-press like machine. (Web presses, the way all thoes unsolicited catalogs you get are made, so buying in bulk from the Chinese makes it cheap!) They claim a 20+ year lifespan. And they would be WAY cheaper than the Ovonics Uni-Solar products.

The only 'problem' is the back-end electronics are still "expensive" and will remain so, even if panels drop from the present price of $5+ per watt to $1. The panels will just be the cheapest part in such a system. Now, if you were powering, oh say, 48 VDC or 12VDC computers, the interface electronics could be as simple as a diode.

If the 1500 ft^2 house is two storey then this is about 75m^2 plan area. The roof area, if pitched, will be somewhat more than that, but the angle ofthe sun at various points will also affect the energy per square metre. A full analysis would involve latitude, pitch angle, etc., but let's assumethat the roof area and sun angle is such that it is perfect all day. At 6% efficiency it might generate 4kW. This would be enough to run the peakdemand of an air conditioning unit in a house in a warm part of the USA if the house was not well insulated. This is with the entire roof covered inpanels, which would be very expensive. So at 6% efficiency it doesn't look to be a good bet. At 20% efficiency then you'd be generating more like12kW, which is respectable, except that your roof/weather/orientation/latitude would be such that you would not achieve this over the whole day andevery day.

So the first measures should be effective insulation (walls and ceiling) and energy efficient appliances and systems. The $ return per $ spentis better.

Having done this it is then worth looking at what residual power needs you have. If you need hot water than you'd be better off withsolar thermal on part of the roof as the efficiency is higher, and a well insulated hot water tank is a very cheap way of storing energy. If youare almost never in during the day then PV panels might not make sense as they would be generating power when you are elsewhere, unless you eitherhave a storage mechanism, or you are exporting your power to a grid or microgrid. If you live in a windy area then for windy winter nights thena roof-mounted wind generator might be appropriate.

On the other hand if you are retired and home most of the day but go to bed early then on top of the solar thermal PV panels might make sense.

It all depends. There's a good case for microgeneration of electricity on offices, malls, etc., that are in use during daylight hours, possiblymore so than solar thermal as you'd never use all that hot water. For a health spa, though, solar thermal to warm that swimming pool would beideal.

It's all about appropriate measures, but almost always the first measures need to be energy efficiency - insulate, and reduce power usage inappliances (e.g. fridges, which are improving dramatically, and LCD TVs which now use about half the power compared to an equivalent screensize CRT).

There are other promising techniques of harvesting sunlight, to only give a small sample: this one [physorg.com] uses buckyballs and gets 5.2% efficiency, and something sort of similar using pentacene [physorg.com] has similar promises, and this one [physorg.com] uses the all-famous carbon nanotubes to convert it directly into hydrogen (but for now it only works with UV-light)

If this keeps up, we'll probably have a choice from a whole range of efficiencies, and more importand $/watt.

There already are [oksolar.com] companies out there that sell solar shingles. They're not economical yet for most applications, but it's starting to come.

but SiO2 is a BITCH to break apart (the usual reaction is with carbon in an almost 2000 deg C arc furnace)

You are partially right... I worked on a project where we were testing a new arc furnace design for smelting silicon (it was a DC furnace as opposed to AC). Wearing one of my hats on that project I wrote a computer model program of the mass and energy balances that took place in the furnace.

My application of the physical chemistry and calculus have passed the haven't used it/lost it point, but if I remember some of the basic things correctly... basically yes it is a real bitch to actually split the silicon (Si) from the oxygen (however, silanes are not involved). It takes a tremendous amount of energy to do so. One of the reasons silica (SiO2) is so abundant is that it is so stable. Being so stable means that it is hard, thermodynamically and every other way, to break it apart. So while Silicon (Si) in the form of Crystaline Silica (SiO2, e.g. quartz, silica sand) is VERY abundant, Si on its own is VERY VERY rare. SiO2 is so much more stable than Si.

Typically the furnace at its hottest point will be around 5000 degrees C (a carbon monoxide plasma forms there).

The silicon metal at the furnace spout where it is tapped/poured from, is typically around 1400 - 1500 degrees C

The reaction is SiO2 + 2C -> Si + 2CO

The intermediate product includes SiO (silicon monoxide which only exists in gas phase at greater than 1400 degrees C) and SiC (silicon carbide).

Most of the actual reaction steps forming the silicon (from silica) happen in gas phase at obviously very high temperature.

The actual smelting process (chemically) is similar to smelting iron: reducing the base metal (removing the oxygen) using carbon as the reducing agent at very high temperatures. (Silicon higher than for iron.)

There are no silanes involved as you describe in the initial smelting process from SiO2 to Si.

With respect to the parent post about silanes: they are possibly created/used later if the silicon needs to be refined to semi conductor grade, but I don't know. I was not involved in this aspect of silicon refining, which is highly proprietary, and which I believe is (or was) protected by laws relating to national security).

The greatest use of silicon is not in electronics. It is in the making of synthetic rubber. e.g. silicone

When it cools, it forms a metallic silvery solid that is very brittle, similar to bituminous or anthracite (hard) coal... which makes sense as it is in the same family as carbon. If you hit it with a hammer it breaks or shatters.

The main raw materials in smelting silicon are typically quartz, coal, and charcoal (and sometimes other more porous carbonaceous materials to improve gas permeability in the reaction bed. The coal and charcoal is for carbon content, not heat. The quartz needs to be quite pure... e.g. no or very very little iron etc in it (brown stains on quartz are typically from iron... not from wayward hikers.

In most silicon furnaces the top of the furnace mix is exposed to atmosphere, and is so hot the carbon monoxide (CO) off gas burns to CO2, which is inert/non poisonous (CO is as flammable as methane, but it is so poisonous that it is not practically safe to do so). Granted the large volumes of inert CO2 created is bad, but better than highly poisonous CO.

An interesting point is if you spill enough molten silicon onto a piece of iron/steel so that the iron starts to melt, the resulting reaction forming Ferro Silicon is so hot that it keeps reacting until one of the reactants is used up (e.g. until no more silicon or iron), or it hits enough of a heat sink to cool to solidification. We had a spill once that took out about 10 yards of the rail tracks some of our equipment rolled on, as well as some other pieces of steel equipment. All of which we needed to re-install or re-build in a couple of hours. Quite exciting, and a huge pain in the ass.

I've seen the Miasole production facility and had a chat with the CEO and one of the engineers at the end of the summer. There're a few interesting things that TFA doesn't mention. First, Miasole claims the low $25M price tag for a 200MW factory because they build all of their equipment from scratch. When I was on the floor, they were building a single 25MW line which they turned on for testing last month. That cost them a grand total of $4M (in parts) to build. E.g. they've already done one, so the pricing is reasonably accurate. Subsequent lines will be cheaper. This will give them a huge cost advantage over other similar companies.

Secondly, their production process is cheaper not only because material costs are lower, but also because they use a "reel-to-reel" process in which the semiconductor material is deposited on a sheet of steel which unrolls into the line, and then rolls back up on a reel on the other side. The steel sheets can then be cut and woven into a vinyl enclosure which can be rolled out on your roof like regular roofing shingles. Cool stuff. (They're probably going to attack industrial markets first though...)

Third, the management team comes from the disk drive industry, and built the Seagate facility that is responsible for ~30% of the world's hard drives (could have the percentage slightly wrong, but is in the ballpark). Hard drives use a similar thin film deposition process, and they have built several other manufacturing systems based on thin film processes. This is why the are able to get such a low cost on their equipment: they have the contacts and expertise to build from scratch.

For the record, I have not talked with their competitors, so I don't know the whole story, but Miasole seems very well positioned, and their facility is certainly real.